1. Field of the Invention
This invention relates generally to digital control systems for electronic apparatus and, more particularly, to digital control of internal circuitry of television receivers and video tape recorders by digital data.
2. Description of the Background
There are now well known various kinds of video and audio equipment, such as television receivers, video tape recorders, and audio tape recorders in which there are digitally controllable internal circuits. Many of the examples of such digitally controllable electronic apparatus have adopted internal bus systems. Typically, an internal bus system includes a central processing unit (CPU), an internal bus, and a read only memory (ROM), which are located within the electronic apparatus. The read only memory may be considered as part of the central processing unit and is used to store the operational information for each of the various internal circuits, In normal operation of such known electronic apparatus, the central processing unit reads the operational information out of the read only memory and transmits such information to the corresponding operational circuit over the lnternal bus lines, so that the corresponding internal circuit properly performs its predetermined operation. Typically, further means of control is provided for each of the internal operational circuits by providing a keyboard or remote controller that can communicate over the internal bus lines with the various internal operational circuits. Both a two-wire bus and a three-wire bus have been advantageously used in such internal bus systems. This kind of internal bus line system is disclosed in Japanese Patent Application No. 57/106262, and it is known that in the three-wire type system the bus lines comprise a data transmission line, a clocksignal transmission line, and an identification signal transmission line, in which the identification signal is used to specify a data block. In the two-wire bus, only a clock signal line and a data signal line are typically provided.
By using an internal bus system, it is possible to substantially simplify the internal wiring that is required to interconnect the various operational circuits in the electronic apparatus and, moreover, testing, manufacturing, and servicing of the electronic apparatus can be carried out using a software approach that further reduces the costs involved. Thus, in utilizing an internal bus system, it is possible that testing, adjustments, and manufacturing can be standardized universally and are so facilitated that overall economic reductions, including lowered manufacturing costs, can be achieved. Accordingly, multi-purpose, high-performance electronic apparatus can easily be fabricated by interconnecting numerous internal operational circuits with an internal bus.
This type of internal bus system is highly suited for use in systems having a plurality of central processing units and a plurality of internal operational circuits controlled by such central processing units, in which the central processingunits are typically referred to as masters and the internal circuits as slaves. Generally, at least one master is incorporated into the specific digitally controllable electronic apparatus and an external master is provided to be connected to the internal bus of the electronic apparatus through an external terminal. Typically, such external master is a so-called microcomputer.
Because the masters and slaves all use the internal bus lines, data communication among the various masters and slaves can be carried out in units of blocks, which define the bus utilization interval, and with such blocks being delimited by start information, such as a specific signal pattern that indicates occupation of the bus, and subsequent stop information. In that case, one master issues the start information to declare that master a controller, sends the address information of one slave to select the control object, transmits the control data or receives data to or from the slave to perform the predetermined control or monitor or check the operation, and then finally transmits the stop information to declare that the master is no longer the controller. In one format accomplishing such operation the rising edge of the stop information pulse indicates that the occupation of the internal bus by that master has ended and that the bus has been released.
Generally, time margins are provided between each block of data transmission, so that any one of the masters can become the controller by interrupting during a time margin. Nevertheless, in cases where an automatic adjustment loop is formed with the slaves, or an external master including an adjustment computer is connected to the adjustment loop, or when an open-loop adjustment is carried out by means of software, an internal master will often interrupt to start its own control when the bus is released midway through the series of data transmissions. In such situation, the external master then loses control and passes to a stand-by state and the adjustment operation does not proceed as desired. In a worst case situation, intermediate data might be destroyed so that the adjustment cannot be completed.